Tunable Filter Technology

Due to the fast development of modern microwave communication system, researches on new kind of cavity microwave filter have attract the attention and research passion of more and more scholars. Mechanical tunable microwave filter is one of them. This kind of filter have been widely used in the range of microwave communication system, which locates in front of antenna in transmitter as to the latter level filtering. Its location behind antenna in receiver is able to inhibit all the disturbing signal and select the useful signal spectrum from all the spectrum that antenna received. Therefore, the design of tunable cavity filter has become a crucial subject.This mater thesis studies the mechanical tunable cavity filter in terms of requirement of realistic projects. We aim to design a kind of cavity microwave filter which realizes continuous change of center frequency by outside mechanical adjustment. Firstly, according to the basic theory of microwave filter, this thesis researches the normalized low-pass principle of filter and principle of frequency transform. Secondly, we discuss relative theory of mechanical tunable filter, introducing the coupling hole model which on the side of the filter cavity and the bandwidth equation of tunable cavity filter deduced by this mode and discussing the relationship between outside Q and coupling coefficient and response characteristics of filter. Finally, based on these theoretical research, we propose a particular single resonant cavity structure and devise a new type of mechanical tunable cavity microwave filter by experiment on plan1and adjustment of plan2. Through analog simulation design and debugging, we realize continuous change of center frequency from2500MHz to2650MHz. Furthermore, the absolute bandwidth of filter remains unchanged at about15MHz when outside mechanical adjustment changes center frequency. Return Loss in passband stays below-20dB. The measurement shows that each indicators of the filter meets the demand.